1. Field of the Invention
This invention relates to a remote optical designator system and, more particularly, to a designator system employing a portable hand-held energy source which identifies specific points or areas of a display such as that on the faceplate of a conventional cathode ray tube, flat panel, or photographic display.
2. Description of the Prior Art
There are many situations where it is advantageous to identify a point or circumscribe an area on a displayed image from a location removed from the faceplate through which the image is viewed. In some known systems a "light pen" is used to identify certain points or areas on the faceplate of a CRT and this system may include apparatus providing an input to a computer which processes the information and then may readout the results on the same CRT. Often the computer provides an optical feedback to the user in the form of a cursor on the faceplate of the CRT which provides a visual indication of the point or points identified by the "light pen".
One such system is disclosed in U.S. Pat. No. 3,441,722, issued Apr. 29, 1969 to P. Gloess for SYSTEM OF COMMUNICATION BETWEEN MAN AND MACHINE. Two orthogonal pairs of photoresponsive elements are disposed around the perimeter of a cathode ray tube. The tip of the pen is grooved and pointed so that light emanating from the phosphor on the inside of the cathode ray tube can be scattered in a planar fashion toward the perimeter of the faceplate. The electrical signals, via the incident light on the photocells, are used to generate a cursor to designate the particular location of the light pen on the faceplate of the CRT.
A particular problem with this and other similar systems is that the "light pen" is a passive element and only reflects or detects local light generated by the display. This means that unless light is routinely generated across the entire display, such as by the scanning electron beam of a CRT, the computer cannot "see" or respond to all possible locations of the light pen. Since a displayed image normally comprises a series of light and dark areas, the light pen can only identify those points in the image which are light. This problem is even more apparent in "stroke-write" display system since the electromagnetic beam of the CRT is not routinely scanned in a predetermined manner as it is in a video display system. In a designator system used with a stroke-write display, it is normally necessary to initially move the light pen to a light spot, such as a cursor displayed in one corner, and pull the cursor to the area of interest in order to read information into the computer.
Another problem of the designator systems employing the passive type of "light pen" just described is that the light pen must be held in close proximity to the display image to reflect light toward the pickups around the perimeter of the display. In the situation where the displayed image is particularly large, i.e. where it is to be viewed by a number of people, a passive "light pen" becomes difficult to use. These systems expand the displayed image from a small source, such as a conventional CRT, by optical means and present it to the diffusing surface of a large display area where the enlarged image is viewed. Because of the small source and its physical separation from the viewing area, the passive type of "light pen" is not suitable for use with this type of system.